Hose assemblies used to carry fuel and other corrosive materials are well known in the art. Such assemblies are exposed to a variety of fuel mixtures, fuel additives, and caustic materials in addition to being exposed to extreme temperatures. Thus, such hose assemblies must be resistant to chemical, environmental, and physical degradation as a result of chemical exposure, environmental exposure to heat, and physical degradation resulting from bending and repeated movement or forces applied to the assembly.
Polymeric fluorocarbon materials such as polytetrafluoroethylene possess the requisite chemical and temperature resistant properties for most fuel hose applications. Unfortunately, polymeric fluorocarbon materials exhibit relatively poor tensile and hoop strengths. As a consequence, such fluorocarbon materials are prone to kinking. The kinking, which can easily become permanent, provides a continual resistance to the fluid flow through the hose assembly.
A well known approach to providing kink resistance to a hose is to incorporate convolutions as shown in U.S. Pat. No. 3,023,787 to Phillips et al. The Phillips et al. patent discloses a convoluted hose assembly having a fluorocarbon inner liner constructed of many layers of helically wrapped Teflon® tape.
Convoluted hose assemblies of the type described in the Phillips et al. patent have several inherent drawbacks. Convoluted hoses in general have a strong tendency to elongate; that is, the convolutions flatten as pressurized fluid moves through them, and this flattening causes the hose to grow in a longitudinal direction. More specifically, because the inner liner in the Phillips et al. hose assembly is formed by helically wrapping layers of a fluorocarbon tape, the seams created by this wrapping are inherently weak and prone to leakage and bursting under internal pressures and prolonged movement. In addition, the seams create undulations within the inner liner which cause disruption in the flow of liquids therein which could give rise to increased electrical charge buildup within the hose.
There are also strong disadvantages inherent in known methods of making convoluted hose. Existing methods are wasteful of costly fluorocarbon materials. In the type disclosed in the Phillips et al. patent, the convolutions are formed by crimping a length of hose straight hose, resulting in a much shorter hose as the end product. The creation of a tube from overlapping winds of tape also wastes expensive materials in the regions of overlap and requires complex, time consuming and labor intensive steps. Finally, hoses of the type disclosed by Phillips et al. do not lend themselves easily to production in a single, continuous, integrated process.
Therefore it would be desirable to have a convoluted hose assembly which with properties of resistance to kinking, bursting, and elongation that are superior to those of existing convoluted hoses. Further, it would be desirable to have a method of making such a convoluted hose assembly in a simple, continuous process, without introducing internal seams, while minimizing the use of costly fluorocarbons and labor in the construction process.